The present invention relates generally to a circuit breaker. More particularly, the invention relates to a puffer type gas circuit breaker having an insulated nozzle formed of heat proof resin and guiding arc extinguishing gas, and thus being suitable as circuit breaker for electric power.
A puffer type gas circuit breaker commonly uses arc suppression sulfur hexafluoride (SF6) gas, which is compressed and is blown between contacts in the process of opening from a closed state, whereby arc occurring between contacts is extinguished to ensure that a large current can be interrupted.
A common configuration of the aforementioned puffer type gas circuit breaker will be described with reference to FIGS. 4 and 5:
FIG. 4 shows that the circuit breaker is closed, while FIG. 5 depicts that the circuit breaker is in the process of opening.
In the closed state illustrated in FIG. 4, a fixed arc contact 1 is in touch with a movable arc contact 3 and is engaged with each other, hence a current path is formed between fixed arc contact 1 and movable arc contact 3.
The movable arc contact 3 together with an arc suppression gas feed insulated nozzle 2 is mounted on the puffer cylinder 4 and is locked therein. An insulated operation rod 6 is connected to this puffer cylinder 4. Accordingly, the insulated operation rod 6 is moved in a predetermined direction (lateral direction in this Figure) by an operation mechanism (not illustrated), whereby the insulated nozzle 2 and movable arc contact 3 are also fed in the lateral direction together with the puffer cylinder 4. Thus, closing operation and breaking operation are performed.
In this case, a puffer piston 5 is fitted in the puffer cylinder 4 and is locked at a fixing section (not illustrated), whereby a puffer chamber 7 for compressing arc suppression gas is formed in the puffer cylinder 4.
The parts constituting an arc suppression chamber are incorporated in an enclosed vessel (not illustrated) serving as a main unit of the puffer type gas circuit breaker. After they have been assembled into a puffer type gas circuit breaker, the enclosed vessel is filled with arc suppression gas such as sulfur hexafluoride, whereby a puffer type gas circuit breaker is formed as a complete product.
The operation of this puffer type gas circuit breaker at the time of opening is performed when the puffer cylinder 4 is driven in the right-hand direction by the operation mechanism through the insulated operation rod 6. Then the state shown in FIG. 4 shifts to the state of opening as shown in FIG. 5.
In this case, the movable arc contact 3 in the state of conduction is opened from the fixed arc contact 1 so that arc A occurs between them. In this case, arc suppression gas in the puffer chamber 7 is compressed and is led into by insulated nozzle 2 to be blown on arc A so that suppression of arc A is promoted with the result that arc A is quickly extinguished and current is interrupted.
Insulated nozzle 2 is commonly made of heat proof resin such as ethylene tetrafluoride resin. When the insulated nozzle 2 is exposed to arc A, energy radiated from arc A breaks into insulated nozzle 2 itself, and is absorbed therein. Then a void or carbonization occurs to the material of insulated nozzle 2, with the result that the creepage insulation performance of insulated nozzle 2, hence interpolar insulation performance, is deteriorated.
To solve this problem, proposals have been made to mix powdered inorganic material into the heat proof resin constituting the insulated nozzle so that energy radiated from arc A is prevented from entering the insulated nozzle 2, whereby arc proof characteristics can be improved. Here mixing of inorganic material can also be called filling with an inorganic filler.
According to Japanese Patent Application Laid-Open No. 49(1974)-17657, Alumina (Al2O3) is recommended as an inorganic material to be mixed, and according to Japanese Patent Application Laid-Open No. 48(1973)-38216, calcium fluoride (CaF2), magnesium fluoride (MgF2), lead sulfide (SbS), barium sulfate (BaSO4) and boron nitride (BN) as such.
Various other suggestions have been proposed regarding the form of mixture of these inorganic materials, in addition to mixing of the inorganic material at a certain density throughout the insulated nozzle. For example, Japanese Patent Application Laid-Open No. 5(1993)-94743 discloses that an inorganic material is mixed up to a certain distance from the inner diameter side in the direction at a right angle to the insulated nozzle axis.
Japanese Patent Application Laid-Open No. 5(1993)-74287 discloses that the type and density of the inorganic material to be mixed are changed stepwise with respect to the distance in the direction at a right angle to the axis. Japanese Patent Application Laid-Open No. 7(1995)-296689 discloses that multiple areas with different mixing densities of inorganic material are provided with respect to the distance in the axial direction of the insulated nozzle, and areas with densities varying continuously among the aforementioned areas are provided.
The aforementioned prior art fails to pay attention to the reduction in the amount of inorganic material, and raises the problem of an overall cost increase in a puffer type gas circuit breaker.
In general, heat proof resin containing such an inorganic material as BN is considerably more expensive than a single heat proof resin. Accordingly, insulated nozzle production cost will be increased by a large amount of mixture.
In the prior art insulated nozzle, however, inorganic material is mixed on all the portions on the side of a puffer cylinder ranging from the upstream to downstream sides with respect to the distance in the axial direction of the insulated nozzle. Production cost is increased by a great amount of inorganic material.
Thus, an object of the present invention is to provide a puffer type gas circuit breaker characterized by a sufficient cost reduction and excellent arc resistance ensured by mixing inorganic material in the insulated nozzle made of heat proof resin.
The above object can be attained by the present invention which provides a puffer type gas circuit breaker with an arc suppression gas feed insulated nozzle made of heat proof resin on the periphery of a movable arc contact characterized in that;
the area in the vicinity of the throat of this insulated nozzle is made of heat proof resin containing an inorganic material, while the portion except for the aforementioned area in the vicinity of the throat is made of heat proof resin without inorganic material;
wherein the aforementioned movable arc contact has a movable arc contact cover for arc suppression gas feed made of heat proof resin between this movable arc contact and insulated nozzle; and
the downstream area of this movable arc contact cover is made of heat proof resin containing inorganic material, while the upstream area is made of heat proof resin without inorganic material.
Here the aforementioned portion of the insulated nozzle made of heat proof resin without inorganic material can constitute the downstream and upstream areas except for said area in the vicinity of the throat. Alternatively, the aforementioned portion of the insulated nozzle made of heat proof resin without inorganic material can constitute only the aforementioned upstream area of the throat.